(1) Field of the Invention
The present invention relates to an image forming device such as a printer and a copier, and in particular to technology for controlling execution of a print job in an image forming device that has a duplex printing function and suspends execution of a printing operation to allow internal temperature of the device to decrease when the internal temperature increases and reaches temperature at which toner in a developing unit is fusible.
(2) Related Art
In recent years, toner that fuses at low temperature has been used in an image forming device such as a printer and a copier, for the purpose of reducing energy consumption. Such toner should fuse due to a heat fixing operation, but is likely to fuse due to an increase in internal temperature of the device. Especially in an image forming device having a duplex printing function, toner is likely to fuse because a recording sheet having been heated due to a heat fixing operation performed on one side thereof in a fixing device is circulated and conveyed in the image forming device, and, as a result, the heat of the recording sheet is transferred to the toner in a developing unit.
To address this issue, an image forming device having a duplex printing function suspends a printing operation to allow the internal temperature to decrease, when the internal temperature increases to predetermined limit temperature at which toner is fusible due to frequent execution of a duplex printing operation and other causes (Japanese Patent Application Publication No. 2009-237119).
With this configuration, since the internal temperature is controlled so that toner in a developing unit does not fuse, it is possible to effectively prevent such problems that the toner in the developing unit fuses due to an increase in the internal temperature, and, as a result, an image forming operation is interfered with and image degradation and other troubles occur.
In the above-mentioned image forming device, however, a printing operation is suspended when the internal temperature increases. For example, when print jobs for performing duplex printing are received in succession and then print jobs for performing simplex printing are received in succession, if these print jobs are executed in the order in which they have been received, the internal temperature soon reaches temperature at which toner is fusible, due to continuous execution of the print jobs for performing duplex printing. As a result, a printing operation is suspended soon. This leads to such problems that the number of printing jobs completed before the suspension is reduced, and thus efficiency of a printing operation before the suspension is not improved.